Robbers in Greece have stolen dozens of artefacts of "incalculable value" from a museum in Ancient Olympia.

Local officials said the Archaeological Museum of Olympia was attacked by armed robbers.

The museum, which is known as the birthplace of the Olympic games, was hit in a planned attack on Friday at around 7.30 am.

The thieves broke in using hammers, according to local media reports.

They tied up and gagged the one female guard present on site and stole up to 60 and 70 artefacts, according to police.

Local mayor Thymios Kotzias suggested two men in masks overpowered the one guard on duty, according to the BBC.

Culture minister Pavlos Geroulanos has apparently offered to resign over the incident, said Skai TV.

British officials are due at the museum on May 10 to light the Olympic torch ahead of this year's summer games in London.